The primary goal of the proposed research is to further our understanding of the nature and basis of the development of intermodal perception of audible and visible events in infancy. Prior research has primarily focused on identifying the nature of cross-modal invariant relations detected by infants. Their findings have been consistent with Gibson's invariant-detection view of perceptual development, but they have left many important questions regarding the nature and basis of intermodal learning and development unanswered. The proposed research will fill this gap by examining the process of intermodal learning directly in a new intermodal training and transfer method. Infants of 2-6 months will receive training with natural, audible and visible events and then the audio-visual relations detected through training will be assessed under a variety of conditions. Three levels of nested audio-visual relations that characterize the stimulation from single events have been delineated: temporal synchrony uniting the sights and sounds of an object's impact, temporal microstructure specifying the composition of an object, and modality-specific relations between the pitch of a sound and the color and shape of an object. This research will identify the developmental progression of infants' detection of these nested relations, providing the first test of whether intermodal learning of nested audio-visual relations proceeds in order of increasing specificity, or in some other developmental sequence. Further, through a series of transfer of training studies, this research will provide the first assessment of how and under what conditions intermodal knowledge acquired in one stimulus context becomes flexibly extended to new event contexts. The attainment of this sort of flexible rule-based knowledge is the essence of intelligent functioning. An understanding of this process will promote the development of norms for intermodal functioning and transfer of training at various ages in infancy. Consequently, one can eventually diagnose abnormal patterns of development.